From 94509f50d696bff745fe26457ce421cea8525bee Mon Sep 17 00:00:00 2001 From: "Guilherme G. Piccoli" Date: Wed, 19 Aug 2026 15:31:30 -0300 Subject: [PATCH] docs: panic: Disclaimer about console verbosity when using panic_print with pstore Users of panic_print / panic_sys_info are usually aware of the potentially huge amount of information displayed with such options - their goal by using them is indeed to dump more information during panic! What might come unnoticed at first is the impact that the console_verbose() call on panic path has, specially in cases that users rely on pstore as a means to collect the panic logs. Recent experience shows that dumping all tasks in an ARM64 system (with qcom_geni tty driver) gets a 2 minute delay on panic time due to writing such information to console. But in that case, pstore was used, so there was no need for console printing, and suppressing that reduced the full time to less than 0.5 second. The option "printk.console_no_auto_verbose" aims exactly at this use case: avoid automatically increasing the loglevel during panic path. So, let's officially document this to avoid users wasting their time either on long panic printing or debugging the panic delays. While at it, improve the readability of the panic_print text, by adding some line breaks. Suggested-by: Petr Mladek Reviewed-by: Bradley Morgan Reviewed-by: Feng Tang Signed-off-by: Guilherme G. Piccoli Reviewed-by: Petr Mladek Signed-off-by: Jonathan Corbet Message-ID: <20260819183419.2203903-1-gpiccoli@igalia.com> --- .../admin-guide/kernel-parameters.txt | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 37c645f36a57..63e65e3ee85b 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4859,6 +4859,7 @@ Kernel parameters panic_print= Bitmask for printing system info when panic happens. User can chose combination of the following bits: + bit 0: print all tasks info bit 1: print system memory info bit 2: print timer info @@ -4867,10 +4868,16 @@ Kernel parameters bit 5: replay all kernel messages on consoles at the end of panic bit 6: print all CPUs backtrace (if available in the arch) bit 7: print only tasks in uninterruptible (blocked) state - *Be aware* that this option may print a _lot_ of lines, - so there are risks of losing older messages in the log. - Use this option carefully, maybe worth to setup a - bigger log buffer with "log_buf_len" along with this. + + *Be aware* that this option may print a _lot_ of lines. + + There is an increased risk of losing older messages in + the log. Maybe worth to setup a bigger log buffer with + "log_buf_len" along with this. + + Also consider using "printk.console_no_auto_verbose=Y" + if using this along with pstore, to avoid extra delays + due to increased console verbosity during panic. panic_sys_info= A comma separated list of extra information to be dumped on panic. @@ -4885,7 +4892,9 @@ Kernel parameters all_bt: print all CPUs backtrace (if available in the arch) blocked_tasks: print only tasks in uninterruptible (blocked) state - This is a human readable alternative to the 'panic_print' option. + This is a human readable alternative to the 'panic_print' + option above. Please be aware of the caveats using this, + check the 'panic_print' parameter for more details. panic_console_replay When panic happens, replay all kernel messages on